1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, particularly to a semiconductor integrated circuit device that includes a decoupling cell that suppresses power noise.
2. Description of Related Art
In recent years, the supply voltage of semiconductor integrated circuit devices has become lower and the power noise has affected more significantly operations of the circuits of those devices. This is why such semiconductor integrated circuit devices have come to include a decoupling capacitor provided between a power line and a ground line to stabilize the supply voltage respectively. The patent document 1 (hereunder, to be referred to as the conventional example 1) discloses an example of such a decoupling capacitor that can be built in such semiconductor integrated circuit devices.
A semiconductor integrated circuit device, when including a plurality of circuit blocks therein, changes the operation mode of each of the circuit blocks in accordance with how the circuit block is used, thereby suppressing its power consumption. For example, the semiconductor integrated circuit device operates each idle circuit block in the standby mode that requires small power consumption and operates each active circuit block in the normal operation mode that requires large power consumption.
The patent documents 2 and 3 (hereunder, to be referred to as the related examples 2 and 3) disclose examples of semiconductor integrated circuit devices, each of which includes a function for switching between such operation modes. FIG. 14 shows a block diagram of the semiconductor integrated circuit device 100 disclosed in the related example 2. As shown in FIG. 14, in the semiconductor integrated circuit device 100, a logic circuit 101 and a power gate switch 102 are connected to each other serially between a power line VDD and a ground line VSS. In the semiconductor integrated circuit device 100, a reference potential line VVss is also connected between the logic circuit 101 and the power gate switch 102. In the conventional example 2, the logic circuit 101 turns on/off the power gate switch 102 according to its operation mode. Consequently, the semiconductor integrated circuit device 100 comes to suppress the leak current in the standby mode, thereby it is assured of fast operations that require large power consumption in the normal operation mode.
In the related example 3, the decoupling capacitor charges the parasitic capacity of the first circuit block when the first circuit block operation mode is changed from standby to normal. Consequently, the semiconductor integrated circuit device 100 suppresses the amount of charge into the parasitic capacity of the first circuit block from the power supply at the time of each operation mode change, thereby suppressing the power noise at that time.    [Patent document 1] Japanese Unexamined Patent Application Publication No. 2005-175003    [Patent document 2] Japanese Unexamined Patent Application Publication No. 2005-268694    [Patent document 3] Japanese Unexamined Patent Application Publication No. 2001-358294    [Non-patent document 1] “Measurement Results of On-chip IR-drop”, K. Kobayashi et al. CUSTOM INTEGRATED CIRCUIT CONFERENCE, 2002, Proceedings of the IEEE 2002, volume, issue, 2002 pp. 521-524